Method of developing multilayer photographic color films



Sept; 1942- K.- SCHINZEL 2,295,013

METHOD OF DEVELOPING MULTILAYEH PHOTOGRAPHIC COLOR FILMS Original Filed April 29, 1937 j BLUE SENSITIVE. FINE GRIT/NED, HYEIEMNY SIL VLI? CHLORIDE FLGLA SENSITIVE TO BLUE VIOLET Z4 SENSITIVE T0 RED AND ORANGEMND lNl'RA-RED) .34 SENSITIVE 7D YELLOW NND GREEN SUPPORT l I I FIGE RED SENSITIVE 2B YELLOW- GREEN SENSITIVE 35 BLUE SENSITIVE (MAYBE TAIYNED) SUPPORT v FLGJC C SENSITIVE T0 BLUE, BLUE-GREEN, GREEN AND YELLOW 2f SENSITIVE T0 BLUE IIND RED (0/? NOT COLOR SENSITIVL? 4f YELLOW FILTER LAYER 3C SENSITIVE T0 RED AND YELLOW SUPPORT RIGID YELLOW SCREENING LAYER FLGLE {IIIIIII,IIIIIIIIIIIIIIIIIIII/fi1 II II/I/II/I/II 1E RED SENSITIVE, UNTANNED 2E YELLOW-GREEN SENSITIVE, TANNED 3E BLUE SENSITIVE. SILVER CHLORIDE, mN/vw SUPPORT IMRL SCHINZEL I l VENTOR ATTORN Y5 Patented Sept. 8, 1942 METHOD OF DEVELOPING MULTILAYER PHOTOGRAPHIO COLOR FILMS Karl Schinzel, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Original application April 29, 1937, Serial No.

139,759. 9, 1938, Serial No. 1936 6 Claims.

This invention relates to a process of color photography of the monopack type, that is, involving the use of differentially color sensitive layers permanently superposed on a' single support, and particularlyto a method of forming colored images in such film. This application is a division of my prior application Serial No. 139,759, filed April 29, 1937.

In the present invention the residual developable silver halide or that formed on the original latent image by general rehalogenation or rehalogenation of each layer is immediately developed to the corresponding final part image, unless other coloring methods are applied for one of the layers. Progress has been made by the present invention since by its diiferential dififusion of re agents into the layers is rendered unnecessary and the process is free from the uncertainties of penetration control and since production ofentirely or almost true color Photographs optically has been made possible without uncertainty and complicated developing machines, and this with the purest vat dyes.

Since production of true-color images by reversal permits an instant control of the successful exposure, I shall, after description of the threeand two-layer systems, describe secondary threecolor development first, and then primary threecolor development, as well as three-color redevelopment and combinations with the difiusion method, with special reference to the production Of three-color negative material. It is understood that the same procedure is also applicable to the making'of prints from autochrome or lenticular screen pictures, especially from those of the bi-pack process and also to printing of three superimposed latent images by means of three separation negatives or diapositives made from them or from bi-pack with insertion of the corresponding filter or by projection on the chromoscope.

Reference will be made from time to time, throughout this specification to the accompanying drawing 'which shows enlarged sections of photographic film embodying certain of my inventions or useful in my improved processes and in which the same reference characters indicate the same elements.

i s. 1, 1A, 1B, 1C, 1D and 1E show sections of film having three diiferentially color sensitized layers on one side of the support-th several figures illustrating difi'erent embodiments.

The three-layer material Referring to Fig. 1, the support S carries the Divided and this application August 223,948. In Austria May 9,

differentially sensitized layers l, 2 and 3, the upperlayer l is generally blue-sensitive, the middle ,layer 2 yellow and the green sensitive and the lower layer 3 red sensitive. In order to limit diffusion to a minimum, it is advisable to make the two upper layers as thin as possible, about 0.0050.01 mm., requiring the use of very finegrain emulsions, relatively poor in silver, for three-color reversal development. In case filter layers t and 5 are interposed, strongly swelling gelatine may be used for these, so that the individual layers are separated by the proper distance from each other during the chemical re-' actions. These filter layers are kept so thin, 0.01 min, 'or less, that harmful difi'usion is not in creased, even if they should swell, to ten times their size. The lowerlayer can 'have the normal thickness of 0.02 mm. for reversal development OBI-0.015 mm., so that the total thickness of the three layers is 0.025-0240 mm. While the twoupper layers require developers 'which' deposit especially productive and intensive dyes on the image, less intensity is required for the lower layer, since this layer may contain considerably more silver halide than the upper and also middle layers. A similar intensity balance of the separation images is often obtained by addition of sulfite to the reversal developer for th lower layer, while this is omitted for the other layers.

In order to obtain a vigorous, well-graded blue image, which is of primary importance for the character of the color photograph, coating of the lower red-sensitive emulsion (for printing, also infrared-sensitive) of an average thickness of about 0.02 mm. using a highly sensitive emulsion of medium soft gradation, preferably sensi- 'tized only for red and orange, is recommended.

Above this, a yellow and green-sensitive emulsion of medium sensitivity and a thickness of not more than 0.01 mm. is coated and over that a sensitized emulsion of also medium sensitivity and not color sensitive and a thickness of 0.005-0.0l mm. For this purpose, transparent, coarse-grain silver bromide emulsion can be used.

" Finest grain emulsions are, however, to be preferred, because their blue and blue-green sensitivity has been strongly increased by recent sensitizers so that the speed of all layers is of the same order. I

The emciency of these sensitizers can be materially increased by ultrasensitization and-hypersensitization" or according to the British Patent 385,545, and this is especially important if in 1 the upper layer a pure silver chlorineor silv er chloroebromide gelatine emulsion is used,"capable -proposed for hyperof being sensitized by the sensitizer of the Br, P. 376,746 to ten times normal, and by ultrasensitization to 50 times normal, not much less by pina flavol. If the finest-grain silver chloride emulsion is arranged in the middle, its sensitivity for yellow-green is already sufficiently high with the usual sensitizers, just as with silver bromide, and this is strongest if some ammonia or also soluble silver salts are added to the emulsion, as has been and ultra-sensitization. This increase in sensitivity is sufiicient for exposures, if modern high-aperture optics are used.

The classical succession of the three layers can be changed, as shown in Fig. 1A, if a very sharp blue imageis desired, by having the upper emulsion IA sensitive to blue-violet, the middle emulsion 2A to red and orange (or infrared) and the lower emulsion 3A to yellow and green;

in which case they are developedlemon-yellow, green-blue and purple respectively. It is less desirable to arrange the layers as shown in Fig. 13 so that the upper emulsion IB is red sensitive, the middle emulsion 2B yellow-green sensitive and the lower emulsion 3B blue sensitive, even if red sensitizers are produced today which in stronger concentration sensitize better for red than for blue' (and this effect can still be increased by adding desnsitizers for blue).

These variations have been made possible, because many of the modern red sensitizers do not sensitize to green and yellow, and because today also those sensitizers can be synthesized which only, and very strongly, sensitize the extreme orange red, in addition to the genuine red.

Even pinacyanol and other. recent high-colloidal red and green sensitizers are not completely adsorbed by silver bromide, so that on coating of a liquidemulsion on one already dried a difiusion of the dye into the, emulsion must be taken into consideration. This difficulty can be prevented by adding precipitants for the sensitizer to the emulsion converting it into a completely insoluble or at leastnon-difiusing salt; it is doubtful, whether only the dye which is not adsorbed by the silver halide grain, or also that part which is adsorbed, are converted into the non-diffusing salt. It is a fact, however, that even with a great excess of the precipitant the color sensitivity'is not materially affected, so that probably also the insoluble salt attached to the silver halide grain acts as a sensitizer. An amount of sensitizer, found by experience, is added to the emulsion, allowed to react for a prolonged time at ordinary or higher temperatures, and the part which is not firmly adsorbed is washed out, and to this is added -3 times the amount of precipitant theoretically required, and the excess can be removed by washing. In the double-coated double layer discussed later, the film is bathed in a solution of the precipitant after sensitization of the two zones, preferably, however, at the end, if sensitization is to be repeated several times. Rendering the sensitizer insoluble or at least of the part which is not adsorbed is especially important in the grain emulsions and mixtures of differently sensitized silver chloride and silver bromide emulsions later described. Acid sensitizers, as for example, erythrosin, eosin, woolblack 43, which is 2-(fl-naphthylazo) -7-(sodium sulfophenylazo) 8- amino l-naphthol-5-sodium sulfonate, etc., are precipitated by barium, thorium, silver salts, and other organic salts or higher-molecular organic bases as naphthidine, diamino-diphexylamine, tetra-amino-ditolylmethane. quinine, cinchonine, quinoidine, and otheralkaloids, diand tri-phenylguanidine, quaternary salts of naphthoquinolineor naphthothiazol base, leuco-bases of triphenylmethane dyes, and their ieuco-cyanide or those of pyronine and trypaflavine; the best however, are clearing basic dyes which may be easily washed out, as auramine, acridine yellow, benzoflavine, tetramethyl-rheonine (3-amino-6-dimethylamino-9- p-dimethylaminophenylacridine), fiaveosine (9- m-carboxyphenyl 3,6-tetraethylaminoacridine) thioflavine T (6 methyl 2 -(p-dimethylaminophenyl) -benzothiazolemethochloride) etc. As precipitants for basic sensitizers are considered: sulfonic acids and carboxylic acids of highmolecular organic bases and also of nonbasic aromatic carbohydrates and heterocycles, such as diazo light yellow 2G (Schultz Farbstofftabellen, 7th edition, No. 749), di-(p-aminobenzoyl-) J acid, the ureas of two molecules of di- (p-aminobenzoyb) J acid, di-(p-aminobenzoy1-) e-naphthylamine sulfonic acid, .p-aminobenzoylp-phenylene diamine sulfonic acid, analogous to Germaine or bayer 205 (Karrer Organic Chemistry, published by Nordmann Publishing Company, New York, 1938, page 429);- better, however, are products having fewer sulfonic acid groups according to the German Patents 427,857; 483,658; 477,914; .further the sulfonic acids of leuco-triphenylmethane dyes and of the leucocyanides mentioned above, but especially also non-oxidizing ones; further sulfonic acids or carboxylic acids of yellow dyes, especially those which are easy to wash out. sensitizers can, of course, also precipitate each other; erythrosin, for example, by rhodamine, pyronine or pinaverdol; wool black 43 by pinacyanol and other isocyanines etc. The most suitable, however, for precipitation of basic sensitizers, as well as their easily prepared reduction products are complex inorganic acids as phosphotungstic acid, silico-tungstic acid, phosphomolybdic acid, etc. or their salts. It is recommended to use partially soluble silver salts of these complex compounds, since they -act favorably on the sensitivity, especially in the presence of ammonia. According to the silver content of the corresponding salts, 0.3-1 g. of the salt and 3-5 cc. of 10% ammonia are added to one liter of emulsion ready for coating. Another more soluble salt of the complex compound can also be added first and then about half of the amount of silver nitrate necessary for formation of the more or less dimcultly soluble complex silver salt dissolved in the necessary amount of ammonia.

If color development of the residual silver halide is to be done by layers, it may be necessary to prevent destruction or weakening of the color sensitivity by the first developer. This requirement is usually fulfilled by neutral developers, as for example, ferrous-oxalate, ferrous sulfite, amidol, hydroquinone with sulfite and acetone, p-amino-o-cresol, triaminotoluol, p-toluyline diamine, m-cresylenc diamine, a mixture of pamino-phenol with m-toluylene diamine etc., or color developers prepared with weak alkalies as sodium, carbonate, borax, trisodium phosphate, sodium glycocoll, etc. which do not split the insoluble sensitizer salts. Small amounts of precipitants can also be added to the developing and fixing solutions or to the washing water.

In some cases, the sensitivity must become more stable to mild oxidizing agents as cupric salt, persulfate, potassium ferricyanlde, alone or ing of the sensitivity to color or of the general sensitivity should take place through these mild oxidizing agents, this may be restored by bathing in solutions of sulflte, bi-sulfite, hydroxylamine, hydrazine, ammonia and similar weak reducing agents before the exposure of thelayers this is also possible with centrifuged silver bromide. Filter layers and dyes The insertion of a yellow filter, indicated at 4 in Fig. 1, transmitting also red rays, between the blue-sensitive and the middle yellow-green or red-orange-sensitive layers is essential, even if the blue rays are generally absorbed by a yellow filter, because there is no means at present permitting complete suppression of the blue-sensitivity of the two other emulsions. A green filter between the middle and lower layers is always unnecessary and a red-orange filter usually so,

sincemany of the present red-orange sensitizers are without efifect in the green and yellow parts of the spectrum.

Ifthe filter dyes necessary for the division of I the spectrum into three partsare added to the and development of the residual silver halide.

Ammonia increases the sensitivity of emulsions freed from silver with chromic acid by 100 times.

Since most sensitizers which can be used for enormous increase of the blue-sensitivity of very fine-grain emulsions, usually increase simultaneously the green and often also the yellow sensitivity their application in the tri-pack and in the three-layer systems made it necessary to alter the principle .of color separation according to the i invention as follows, reference being made to Fig. 1C: The upper layer IC is sensitized for blue, blue-green, green and yellow and the residual silver halide finally developed by reversal to purple or red, The middle layer is sensitive to blue and red, or only for blue and violet, that is, not color sensitized and the second time'it is developed golden yellow or lemon yellow. The lower layer is sensitive to red and yellow, and its residual silver halide is developed green-blue or blue. A yellow filter layer d-C may be inserted between the middle and lower layer.

. This double sensitivity of each layer for' two entirely difierent spectral regions permits'an essentially better selection than in the previous method, utilizing the film shown in Fig. 1, where the upper layer is only sensitive to blue, the middle layer for green and yellow, and the lower layer for orange and red; or reversed, as shown in Fig. 1A, the middle layer for red and the lower layer for green-yellow, in each of which the residual silver halide is developed to the color complementary to its sensitivity.

An infrared sensitizer as cryptocyanine, neocyanine etc., stable to the correspondingly selected developer can also be added to one of the layers usually to the lower, red-sensitive layer which by second exposure of the residual silver bromide with infrared permits the individua color development of this layer alone.

The emulsions can also be coated on the support in opposite order,if the exposure is made through the back.

velopment and three-color redevelopment.

silver halide colloid layers, namely, yellow to the blue-sensitive layer,'red-orange or green to the middle layer, the true color is to a certain degree affected, because regardlss of the thinness of the layers formation of the latent image only in the upper part of each emulsion layer 'is permitted; this effect is, however, mainly noticeable in reversal development, in primary three-color de- The desirable filter action can also be attained by correspondingly increasing. the amount of sensitizer,

but only with those which in greater concentration do not cause excessive loss of color sensitivity. Strongly swelling gelatine should be used for the emulsions in order to prevent overlapping of the color reactions from one emulsion to another.

The use of intermediate layers as color filters the gelatine layer adjacent to the blue-sensitive sion itself.

emulsion yellow, or also the blue-sensitive emul The, other intermediate gelatine layer, if it is present at all, may remain col'orless or may also be colored yellow instead of red or green.

The whole triple layer with one or two 'mtermediate layers, or without them, may also be colored yellow throughout; most simply, by subsequent'bathing in dye solutions. Bathing need only be done for such a time as is required to color the blue-sensitive and the adjacent layer sufiiciently for complete absorption of all the blue. With partial or complete yellow coloring it is, of course, essential that the red sensitizer sensitize exclusively for red and red-orange with a distinct minimum in the yellow and green region of the spectrum or entirely without eiTect A collodion emulsion highly sensitized by dyes v and coated on a thin film of cellulose acetate,

Cellophane or synthetic colloids, can also be used as the lower layer; or hardened gelatine emulsions, especially those in which part of the gelatine is replaced by agar, polyvinyl alcohol or other less swelling-and, therefore, quickly drying colloids. Thisconcerns mainly the so-called peptization emulsions and similar. procedures in which the silver halide freed entirely "or partially of, gelatine can be sensitized before mixing it with the main mass of the 'emulsifyingagent;

' red-sensitive layer.

in that region, because yellow and green-yellow rays can then penetrate to the lower, usually The yellow dye must in no way effect the sensitivity. In the relatively easily prepared and completely yellow colored triple layer the middle emulsion is protected from the action of blue light on both sides by yellow.

filters'or yellow coloring :of the adjacent silver halide emulsions which is desirable if blue light is to be used for the exposure of regenerated or residual silver halide.

The'middle silver halide layer 2 (Fig. 1D) may also besurrounded by filter or emulsion layers lDand 5 absorbing ultra-violet and containing colorless orcorrectly colored filter-substances over, or yellow coloring of, the blue-sensitive emulsion is essential for reasons stated before, so that only a layer absorbing ultra-violet between the middle and lower layer is used.

The triple layer with yellow colored bluesensitive emulsion or with a special yellow filter layer, or both, or an additional intermediate and colorless gelatine layer, may also be treated after coating in a solution of the substance absorbing ultra-violet. It the present division of the spectrum into three regions is adopted, the amount of filter dye or the intensity of the coloring in all the variations previously described must be adjusted so that as little as possible or no blue light at all reaches the middle layer during exp sure.

It the triple layer contains at least one yellow filter layer or a yellow-dyed blue-sensitive silver of the yellow filter dye into the adjacent layers is perhaps without special detriment, butis best avoided in the interest of as true reproduction as possible; the red filter dye must, however, be water-insoluble or non-diffusing. Filter dyes which are insoluble in themselves and strongly colored substances, but readily soluble in sodium carbonate, alkalles or acids, are most suited.

They are added to the mlatine in a highly dispersed state or are precipitated in it. Watersoluble dyes are added to the layers in form of insoluble saltsor precipitated in the gelatine solution as such. Coloring of the filter layers with water-soluble, substantive and high-colloidal dyes is .also satisfactory without conversion into the insoluble dye salt. Slight difiusion of the dye is harmless, unless it is'capable of sensitizing or reducing the sensitivity. I

synthesized in gelatine solution and soluble in sodium carbonate and alkalies by proper substitution are: azine and phenylhydrazone of alloxone, anils of the hydroxyaldehydes, a-naphthol azo dyes, hydroxy-azo-benzol, and 9.20- phenol, especially also meta-substituted azobodies.

Basic dyes, readily washed out by dilute acids are: auramine, thiofiavine T and other basic dyes suitable for Uvachromie, nitroso-dimethylaniline, azcmethine, anils and related compounds, and especially azo-dyes with amino groups in meta-position.

Splitting anils and analogously constructed arylated auramines, also with aminoand dimethylamino groups, are suitable. Some of them are also converted into soluble salts by addition of bisulfite or thiosulfate.

Azomethines and indophenols, indamines, etc., which also are readily split by dilute acids to colorless compounds or are converted into easily washed salts by addition of bisulfite or thiosulfate.

Diazo-amino compounds are'readily split by acids and the free diazonium salts can usually be easily washed out. O-p-substituted amines are used for condensation in order to prevent the possibility of coupling.

Aryl-azo-hydrozu-auilides are often readily de-v cyanide, red-copperand uranyl ferrocyanide.

These and also the colorless ferrocyanides oi. zinc,

, thorium etc., can also serve as mordants for yel- Solution or destruction of the substances ab-' sorbing ultra-violet is necessary only, it fluorescence is too disturbing in the finished color pic- -tures, or if they discolor on prolonged exposure to light. In the selection of genuine filter dyes,

one must take into consideration that they should be readily washed out or converted into colorless compounds at the end of the color process by means of acids or bases, oxidizing or reducing agents, or by other suitable reagents. Sometimes, this becomes necessary in an earlier stage agent permeable to water may serve as antihalation protection on either side of the base.

The principal filter dyes applied are'those proposed in literature for similar purposes which usually are discolored or washed out by the developer containing sodiumcarbon'ate or by the fixing solution. Other suitable dyes are:

Insoluble dye substances, capable of being low and red basic dyes; after destruction or solu tion of the mordanting bodies, the dyes may beeasily washed out.

Zim-murezide of yellow color is easily discolored by acid. 7

Insoluble complex compounds can'usually be split by dilute acids with loss of the dye character. In certain respects also lacquers of alizarin dyes and of otherhydroxyand dioxyanthraquinones, belong. to this group. Titanic acid yield complexes with phenols and phenolcarboxylic acids which are precipitated by aromatic bases. Hydroxy-guanidine, hydroxy-amidine, biiormamide, guanylformamide, guanylurea, nitroso-fl-naphtholetc. sometimes yield useful colored complex salts with, copper-, nickeland cobalt salts. Isonitroso-aceto-phenone yields yellow complexes with zinc and cadmium. Also complex copper and nickel salts of o-naphthaldoxime and analogous compounds are colored yellow. Phenol, which has the structure:

cmoQ-c o c H3 and the copper complex is green.

A20 dyes split by reduction-Insoluble azo dyes or their sulfonic acid salts of the same composition added to the layers are split by zinc chloride, hydrosulflte and various other reducing aces-01s agents in acid, neutral or alkaline solution, at

the azo linkage with loss of the dye characteristics. This treatment is permissible if the separation color images consist of vat dyes, lndophenols,

various oxidizing agents, such as weakly acidified.

permanganate, persulfate, bichromate, hydrogen peromde, hypochlorite, neutral or alkaline potassium ferricyanlde, etc., are suitable for destruction of the filter dye which may take place simultaneously with the solution of silver. phenylmethane 'dyes, amino-hydroxy-anthraquinones and their sulfonic acid salts, substantive azo dyes or their insoluble or non-difiuslng' salts, vegetable dyes, blossom dyes, fulgides, isocyanines and other quinoline dyes etc. may be very easily destroyed. Dyes with free amino groups are usually not destroyed by acidified nitrite, but

Many tri-.

a diazonium compound of little aflinity to gelatine is formed, so that it can bewashed out still more easily than basic dyes. Light-unstable filter dyes-Many iso-cyanines, fulgides, Besthorns quinadinic acid dyes, certain vegetable dyes, etc., are very unstable to light, especially in the presence of mild oxidizing agents, which makes them suitable for bleaching processes. They may be quickly destroyed therefore, under these circumstances, by illumination of the finished image with ultra-violet light, which is especially suitable for the yellow filter dye easily accessible from above.

Substances absorbing ultra-oioZeL-Sultable substances are aesculine, quinine, anethol, triphenylmethane, cumarone, acetaminoquinoline, hydroxy-quinoline sulfonic acids, hydroxy-naphthoic acids, naphthol-sulfonic acids, naphthylamine sulfonic acids and the analogous substitu-' tion products of anthracene, as well as many others known from the literature, or their insoluble salts, esters, anilides and other derivatives. I 1

Three-color reversal development After exposure or printing exposure, the superimposed latent images are developed to the three 1 black separation silver images'by an ordinary,

' non-tanning, preferably neutral developer, as

ferrous oxalate, amidol, diamido-o-cresol etc. Most other organic developersin solutions containing sodium carbonate are also suitable, since they do not noticeably harm the color sensitivity, and this can be at least partially restored by the proper reagents. There is no emulsion for which the use of the so-called compensation developers for correction of the almost unavoidable difierences in exposure of the individual separation emulsion is more recommended than for the triple layer.

In order to avoid the undesirable effect of local under-exposure in the lower'layers, it is best to bathe all three layers first in a solution of the non-acting developer substance of a considerably images.

Usually, such sensitizers are selected, and this to th first weakly stronger concentration than usual. and then to develop in solutions of sodium carbonate, am-

monia or weak alkalies. Simple concentrated The greatest difficulty is to make-the residual silver halide of the middle layer developable' without influencing the other two existing Part is assumed in the following examples, as are stable, at least to a neutral black developer and alkaline color developer. A special advantage of the invention, however, is the fact that sensitization does not even have to withstand the ordinary general development, it the middle layer is surrounded by two filters which are impenetrable to blue or ultra-violet light which latter makes the residual silver halide of the upper and middle layer developable, while the production of the middle part image is done, even without the action of light, by chemical pretreatment with weak reducing agents or with the use of energetically acting color developers. It

is, of course, assumed that both filter dyes are stable to the developer and are destroyed only later by acids, bases, oxidation or reduction. The lost color sensitivity can be restored by resensitization which, however, complicates the process.

It must not be omitted to mention that the character of the reversal images can be changed to a certain degree by a very careful general exposure or additional exposure through color filters ofall or some of the layers.

The following examples illustrate the practical application of the principles of three-color reversal development as explained in the'preceding paragraphs, reference being made particularly to Fig. 1 by way of example.

In the absence of filter layers and with sensitization of the lower layer 3 exclusively for red or also orange or infrared, the initially reduced silver could be, as also in other cases, converted into silver ferrocyanide which is no more developable or only extremely slowly so with suitable color developers, or into highly dispersed silver iodide, or into any other colorless silver salts which is insoluble, and difilcultly reduced, preferably soluble in hypo, and decomposed by alkali or acid or the metallic silver can be com- I pletely dissolved by oxidizing agents and washed out. Here and in analogous cases discussed later it is sufficient, if at least the highly dispersed silver of the upper layer I and, totally or partially also the fine-grain silver of the middle layer 2 is converted in this manner. Waiting is then not necessary, (and this is a characterizing point of the present invention,l until also the coarser negative silver of the lower layer 3 is converted or dissolved, since exposure of the residual silver halide of the middle layer 2 is best done from above. The residual silver halide of the middle layer 2 is then exposed to yellow or green light from either side and developed purple. After this, the silver halide of the lower layer 3 is exposed to red light through the support S and desions of the upper or also middle layer.

of inability to diffuse.

veloped green-blue. Finally, the residual silver halide of the upper layer I is exposed to blue or ultra-.violet light and developed yellow. A variant or this procedure would be to re-expose the lower layer 3 first to red light and develop greenblue, then re-expose the middle layer to yellow light from above, etc. In all these variants it is assumed that the sensitizers of the middle and lower layers are stable to mild oxidizing agents acting on metallic silver. This condition can best be fulfilled by the presence of highly dispersed silver, as it exists in the highly sensitized grainless or very fine-grain silver halide emul- The color sensitivity can, however, be partially restored by dilute solutions of sulfite, bisulfite, hydrazine sulfate etc., unless addition of these agents with bleaching of the dye already formed does not take place.

The lower layer 3 can also be exposed to red light directly after primary general development and its residual silver halide developed greenblue, and only then all silver which was previously reduced, or at least the highly dispersed silver of the upper layer (or partially, also, the finegrain silver of the middle layer), removed or preferably converted into silver ferrocyanide or the compounds mentioned above. The middle layer alone 2 is then exposed to yellow light from above and developed purple, then the upper layer is exposed to blue light and developed yellow. The exposure of the middle layer 2 to green light from below, or to blue light from below in the case of a yellow filter layer 4 between the top two layers, can be less satisfactorily accomplished by exposing in either case after preliminary reduction of the green blue dye formed in the lower layer 3 to its easily re-oxidized insoluble leucoforms. Reduction of the residual silver halide of the upper layer I may be effected here, as in similar cases, byalkaline solution of the leucoforms of various yellow vat dyes, best under exclusion of atmospheric oxygento prevent fog. Oxidation stability of the red sensitlzer, which may here be also sensitive to yellow, is no more required, which represents a very great advantage compared t the method of execution previously described, because the choice of proper red sensitizers is much less limited, and many may be used which excel by complete insolubility Under certain circumstances, even oxidation-stability of the sensitizer of the middle layer is unnecessary, as proven by th following examples:

The residual silver halide of the middle layer 2 can be exposed also to blue light through the support S, if suiilcient blue sensitivity of the upper layer I was obtained by high sensitization which is then lost during conversion by oxidation of the primarily reduced silver, since here the undesirable effect of the very little sensitive upper layer is not feared. The hardly noticeable difierence conditioned by the lower blue (or purple) image can be corrected by creating a blue (or purple) indo-phenol or azomethine dye in addition to the silver in the first general development which, however, in contrast to the final image dye of the lower layer (indigo, Russigs dye, described in Journal of Practical Chemistry (2) vol. 62, page 53, (1900), seleno indigo etc.) is easily split by acid. After making the residual silver halide of the middle layer 2 developable with blue light through this lower layer now uniformly colored, the intermediate dye of the lower layer is destroyed. This may also be done after completion of the three-color Image, if also the final yellow dye of the upper part image is stable to acid.

As a further example, the middle layer 2 is exposed to yellow light from either side and developed purple, then the upper layer I is exposed to blue light and developed yellow, finally the lower layer 3 to blue, white or red light and developed green-blue after removal or conversion of the primarily reduced silver, 11' there is a yellow filter layer 5 between the middle and upper layer or if the latter is colored yellow and the yellowgreen sensltizer alone is oxidation-stable. The lower layer 3 can also first be exposed to red light and developed green-blue, then the upper layer l to blue light and developed yellow, or in v to develop yellow, or in reverse order, and then only toconvert all silver, or at least that of the upper layer, into silver ferrocyanide or to dissolve it. and finally to expose the middle layer 2 to yellow and to develop purple.

The stability of the green-yellow sensitizer to oxidation is not absolutely necessary for the middle layer 2, if at least the yellow filter layer 4 which also absorbs ultra-violet, or yellow coloring of the upper layer is present, so that in the triple layer, according to the present invention, one can entirely dispense with oxidation-stable sensitizers and pay more attention to prevention of diffusion of sensitizers from one layer to the other. The lower layer 3 is exposed to red light after general black development and is developed green-blue and treated further according to one of the following methods:

It would be simplest to expose the middle layer to ultra-violet light through the lower uniformly blackened layer and through the green-blue dye not absorbing ultra-violet or to infrared light, if it was also sensitized for this in addition to green-yellow, and to develop purple. This requires long exposure, however, since the lower layer absorbs most of the light. Even in exposure of the upper layer to blue light, because the primarily reduced silver prevents a complete exposure through the depth of the upper layer, some residual silver halide will be left and developed in the color of the middle layer, if this is developed later. By the use of ultra-violet light for exposure of the residual silver halide of the upper layer this evil is eliminated, according to the invention. The same efiect is gained with soft X -rays, if the upper part image is produced last.

It is, however, better first to expose the upper layer to ultra-violet light and develop a yellow image. Alternatively it may be treated briefly with a 1 to 2% solution of potassium ferricyanide or with a silver solvent converting or dissolving only the highly dispersed silver of theupper layer entirely or partially into white silver ferrocyanide, without allowing this to take place in the other two layers. upper layer is then converted into a yellow image. The lowest layer is then exposed to red light and developed to blue-green. If two filter. layers 4 and 5 are provided a yellow and a red or orange one, or two yellow layers, exposure of the residual The residual silver halide of the.

silver halide of the lower layer can be done even with blue light. The middle purple part image is then btained by one of the following methods: (a) he residual silver halide oi the middle layer is made developable by pre-treatment with about 0.02% solution of thiourea. thiosinamine etc., or analogously acting sulfur derivatives, or with a 0.001% solution of zinc chloride, by means of arsenlte, hypophosphite, thallo salt, triamido phenol, masking dyes, especially in the presence of heavy metal salts or other suitable agents, which may also be added to the corresponding color developers; it is then developed purple, and finally all silver removed or fixed out. The pretreatment may be omitted, if a color developer is chosen which acts so vigorously on addition of ammonia or alkali, or also alcohol and acetone, preferably without air, that the residual silver halide of the middle layer is reduced without exposure after prolonged treatment. This is especially true for a silver chloride emulsion layer which, unexposed, is suificiently stable tothe color developers containing soda which is necessary for the two outer layers. The residual silver bromide of the middle layer is, however. reduced without pre-treatment or exposure by most leuco-vat dyes in alkaline solution or one containing alcohol or acetone with precipitation of the dye on the image. Residues of the latent images in the other two layers can be destroyed previously by the action of mild oxidizing agents as potassium ferricyanide and ammonia etc.

(b) All previously reduced silver is removed entirely or for the largest part, combining with it possibly the destruction of filter dyes by oxidation or acid, or converting into ferrocyanide etc., exposing the residual silver halide of the middle layer from both sides to white, or better, ultraviolet light or to soft X-rays and developing purple, and finally, removing the silver and fixing out, if necessary, both of which are possible with Farmer's reducer. The residual silver bromide can also be reduced to black silver with vigorous ordinary developer or with any organic or inoranic reducing agent; this is then converted into very easily oxidizable highly dispersed silver chloride by bichloride of mercury with the color developers even without exposure.

light and made developable, then, in any order, the two outer-layers to blue light, or only one ct them in this manner and the other made developable with thiourea etc. in a preliminary bath or as addition to the developer. If the sensitizers of both lower layers are stable to developer, the residual silver halide of the lower layer can also be made developable by red light and converted into the green-blue part color image first. then the middle layer exposed from above to yellow light and developed purple, and finally the upper layer exposed to blue light and developed yellow. It is, howevenmore desirable to make the middle part color image according to the methods described before. 7

Stability of the sensitizers to developer and oxidation agents is not absolutely required, even with intermediate filter layers absorbing ultraviolet, as can be seen from the following examples: I

If a. colorless or yellow-colored layer not transmitting ultra-violet is situated between the upper and middle silver halide emulsion layers, the lower layer is first exposed to red light after general development-and developed in color; then follows exposure from above with ultra-violet light, and the upper silver bromide or silver chloride layer is developed yellow; after this. the middle layer is made developable, according to the above-described methods by intense ultraviolet exposure from the back or better with thiourea etc. and the corresponding part color image is developed. If a yellow filter is on the top and one absorbing ultra-violet between the lower and middle layers, the lower layer is exposed to ultra-violet light and developed greenblue; then, after one of the above-mentioned methods, the upper and middle layers are treated, one of them consisting of silver chloride, and veloped.

If two ultra-violet filter layersare arranged on both sides of the middle silver halide layer dB (Fig. 1D), the outer layer l is first exposed to ultra-violet light and colored, then the lower layer 3, and then with intensive exposure from both sides to soft X-rays or ultra-violet light, (if

(c) The residual silver halide of the middle layer is at once made developable by exposure a from above or from both sides to ultra-violet light or better soft X-rays, and the corresponding part image is developed. This is possible, because very fine-grain and not cohering reduced silver is very transparent to ultra-violet light. The silver is then removed.

The procedures just described and particularly the processing of the lower layer prior to the middle layer are based in the assumption that the sensitizers are not stable to oxidation. Stability to the developer is not necessarily assumed. If, however, at least the yellow-green sensitizer of the middle layer is stable to development and oxidation, all metallic silver of the three layers can be removed immediately after the usual development or it may be converted into silver ferrocyanide. The middle layercan then be ex.- posed from above, or if the lower filter layer is orange, from below or from both sides to yellow light and developed purple; after this, the residual silver halides of the two other layers are exposed to blue light and developed to the appropriate colors in succession. Less complete results are obtained, if the residual silver halide of the middle layer is first exposed from above to yellow green necessary, after removal or destruction of the substance absorbing ultra-violet,) or better by treatment with thiourea etc., the middle layer 2 is made developable and developed in color; finally, all silver and remaining unused salt is removed. The upper layer absorbing ultra-violet can also be colored yellow, for example, by using nitroso-dimethylaniline. The middle layer can, of course, be made developable by white or colored light, according to the sensitivity of the layer after removing the silver of both other layers or converting it into ferrocyanide etc. If it was sensitized for infrared, it is exposed to these rays which readily penetrate the dyes present in the two other layers.

tween the middle and lower silver halide layers,

a yellow filter between middle and upper layers, the lower layer is exposed to ultra-violet rays, the upper to blue light, perhaps, after preliminary conversion of the highly dispersed silver of the the corresponding part color images desame into silver ferrocyanide etc. The ultraviolet-absorbing substances can, of course, also be added to upper and lower sensitive emulsion layer instead of an intermediate layer.

Exposure through the back in all previous cases may be somewhat prolonged, since ultraviolet light is partially absorbed by pyroxylin,

' unless a very thin film or one of material permeable to ultra-violet, such as cellulose acetate or Cellophane, is used.

Since silver bromide must withstand four developments, three of them with color developers containing sulfite-free sodium carbonate or alkali, in order to obtain vigorous part images, fog is difflcult to avoid. It is, therefore, recommended to use an upper or middle silver chloride layer, especially with filmacoated on both sides, where the film itself or a coated filter layer can contain colorless substances absorbing ultraviolet and the red-sensitive silver halide layer is alone on one side, because silver chloride is colored, even if it is not exposed, and still more so unexposed silver bromide. Colored development of the original residual silvery chloride can be even entirely dispensed with, since it is easily converted into silver ferrocyanide and this into colored substances, or easily colored mordanting bodies. One is not dependent upon the easy reducing ability of silver chloride at all, if the residual silver chloride is only temporarily converted into silver ferrocyanide after first general black development; according to the invention. After colored development of the two other layers, it is reconverted into silver chloride or silver bromide, or less desirably, into silver iodide, which can also be effected by addition of potassium bromide, etc. to the last color developer. The residual silver ferrocyanide could also be reduced with a vigorous color developer directly, or with,formation of the color image from silver iodide which is readily obtained from the residual silver chloride.

It is possible to utilize the difierential development properties of silver chloride and bromide to form an image in the silver chloride only. Since silver chloride develops more rapidly than silver bromide, a strongly differential action is obtained particularly when the chloride layer is uppermost. In this case development is ordinarily not carried to completion but is stopped when a usable, even if incompletely developed image, is obtained prior to any substantial development of an image inthe layer containing silver bromide. In such cases other expedients found useful in differential development may also be employed such as the use of retardants or hardening the lower layer.

The later undesired further development of the exposed but undeveloped residue may be avoided by converting the chloride to another salt.

The silver chloride layer only may be developed to a black silver image followed immediately with development of the residual silver chloride with a weak color developer which does not rapidly attack the exposed silver bromide. The residual silver chloride may also be directly or indirectly converted into a colored substance or a mordanting body, as described in detail later. Only then, the two silver bromide layers are simultaneously developed in an ordinary developer, and finally, the residual silver halide of the same developed in succession to the corresponding color, first, after corresponding exposure, the layer which was situated away from the objective, then the other one, after pretreatment with thiourea, stannous salt etc. or with a vigorous color developer.

All this also holds true for a middle'silver chloride layer and is especially favorable with films coated on both sides.

A middle silver chloride layer permits in this manner, independent development of all three part images, even when no filter layer or only one is present and sensitization is not even stable to an ordinary black developer. Several such processes will be outlined. of the middle silver chloride layer is first developed alone with a weak ordinary developer, and then, with a color deve1oper which is only strong enough to reduce the residual unexposed silver chloride, but not the exposed or unexposed silver bromide, the middle part image is developed. For this purpose, the silver chloride of this layer could be pre-treated with solutions of very mild reducing agents or compounds containing sulfur which make the residual silver chloride of the middle layer developable, but not the unexposed silver bromide. since the middle layer is entirely blackened by metallic silver, the two other layers can be independently exrwsed to blue light after ordinary development, and their residual silver bromide can be individually developed in color.

(17) Furthermore, the residual silver chloride of the middle layer can be converted into silver ferrocyanide after usual black development, the latent images of the other two layers developed in an ordinary developer, the silver ferrocyanide of the middle layer reconverted into silver chloride and this silver chloride and the residual silver bromide of one or both layers made developable by exposure, chemical pro-treatment or in any other manner. Now the middle color image is developed with a specific silver chloride developer and the residual silver bromide transformed into the inert state by mild oxidizing agents, as for the destruction of chemical fog, then, by a bath of sulfite, bisulfite, hydrazineor hydroxylamine salt it is made sufiiciently light-sensitive and each silver bromide layer individually exposed and developed in color. The silver ferrocyanide obtained from the residual silver chloride is in itself sufliciently dense to allow the residual, highly sensitive silver bromide of the lower layer to be given a short exposure; a better procedure is to convert with lead chloride or thorium salt into the corresponding ferrocyanides and to convert the newly obtained silver chloride into silver ferrocyanide. All silverferrocyanide could also be converted into lead chromate which acts like a yellow filter in the individual exposures of the two outer silver bromide layers and is removed at the end. All this holds especially true, if the very fine-grain silver bromide of "the upper layer has lost its high sensitivity which it had acquired through high sensitization. The silver ferrocyanide of the middle layer or the zinc ferrocyanide obtained from it with zinc chloride or zinc bromide may serve as an'excellent mordanting substance for coloring with yellow basic dyes, resulting in a middle yellow-black filter. The two latent silver bromide images can now be developed under certain conditions, unless this has been done before, and the residual silver bromide of each layer individually exposed and developed in co or.

(0) After simultaneous development of all three latent images, the residual silver chloride of the middle layer is converted into silver ferrocyanide and this into yellow titanium ferro- (a) The latent image f insoluble ferrocyanide, or also through nickel ferrocyanide into nickel-dimethylglyoxime or other insoluble colored and easily split complex compounds which act as middle light filters in the exposure of the residual silver bromide of. the two outer layers. The insoluble ferrocyanides are split by sodium carbonate or alkali, the complex salts mostly by acids. The silver chloride formed can be reconverted into silver ferrocyanide which is practically insensitive to light, or it is converted with bromine salts, since silver bromide formed in this way is only very slightly sensitive to light in comparison with the silver bromide of the lower layer. After colored development of the two outer layers, silver halide may be regenerated from the silver ferrocyanide of the middle layer and this made developable by thiourea, stannous salt, masking dyes etc. or by intensive exposure to ultra-violet or X-rays, and developed in color or converted, similar to the original silver ferrocyanide, with a vigorous color developer directly into the part color image. Finally, all silver and the insoluble ferrocyanides are removed and the filter dyes washed out.

(d) All three layers can be developed simultaneously and the residual silver chloride converted into silver ferrocyanide and this reconverted into silver chloride which becomes very highly dispersed and easily developable, so that the middle part image is developed by a color developer without exposure. The other part color images are then developed from theresidual silver bromide of the two outer layers. The residual silver halide of all three layers can be made developable simultaneously by ultra-violet or X- rays, by pre-treatment with thiourea etc., and the silver chloride of the middle layer developed in color, so that a homogeneous color filter is created in the middle. The latent developing ability of the residual silver bromide is now destroyed by the-action of mild oxidizing reagents, p-phenylenediamine and acid etc., sufiicient general sensitivity created by a bath of sulfite, bisulfite, hydrazine salt, hydroxylamine etc. or by optical sensitizers in preferably weak ammoniacal solution, and the two outer emulsions individually exposed and developed in color. If the middle emulsion is still sufiiciently yellow-green or red-sensitive after ordinary development of the silver chloride, it is exposed to the proper light and the residual silver chloride developed in color, so that a homogeneous silver filter also results. The latent images are then developed in the two outer silver bromide emulsions, and finally, their residual silver bromide individually exposed and developed to the corresponding part color images. The same holds true, if the sensitizers mentioned do not survive the first general development, but if the middle emulsion contains in addition a reistant infrared sensitizer, so that the residual silver chloride of the middle emulsion can be made developable by infrared rays for which the two outer silver bromide emulsions are absolutely insensitive and which is not harmful to the latent images contained in them. Since a yellow filter between the upper and middle emulsions is indispensable for nature photography, all reduced in the upper silver bromide emulsion; or viceversa. The silver is removed at the end.

(e) If an upper or middle silver chloride emulsion exists it is possible to convert the residual silver chloride into silver ferrocyanide, and only then proceed to general black development of the two silver bromide emulsions. Without preliminary removal of the silver bromide, the lower (or in reverse order for exposure through the back; of the upper) red-sensitive emulsion is exposed to red rays (if a green-sensitive emulsion to green rays) and developed in the approximately complementary color. The residual silver bromide of the middle emulsion is then made developable with thiocarbamide etc. and the corresponding part color image developed. Finally, the silver ferrocyanide of the blue-sensitive emulsion is converted into silver halide by sodium chloride or potassium bromide, which may also be added to the color developer, made developablevby light or repeated treatment with thiocarbamide and developed to the corresponding part color image. All silver is then removed simultaneously. The reconverted silver chloride is highly dispersed and is reduced by correspondingly vigorous color developers, also without exdeveloper and mild oxidizing agents can also be added to this'emulsion or to the silver chloride emulsion. The residual silver halide of this emulsion can be made developable through infrared light, even if the original sensitizer has become ineffective. Any other sensitizer could, however, be added to the lower emulsion in. addition to that for red, for which the middle emulsion is insensitive. An infrared sensitizer which is stable to the developer, can generallybe added to the lower emulsion in addition to the red sensitizer.

After general primary development, the residual silver bromide of this emulsion is first exposed to infrared rays and developed in color, the other two emulsions can then be made developable with thiourea etc., and first the silver chloride, then the silver bromide emulsion developed in color. In printing, the lower emulsion can be sensitized exclusively for infrared, the middle for red, orange, yellow or green, and the residual silver halide made developable-with this light.

Specific action of a developer on silver chloride does not depend on its chemical constitution alone, but even more on the working conditions. P-aminophenol, p-dichloraminophenol, p-aminodimethylaniline develop silver chloride even as tree bases or their salts in the presence of bicarbonate. Amidol and diaminoresorcin can be weakly acidified without losing their developing power for silver chloride. Pyrogalloldimethylether in alkaline solution works much morerapidly on silver chloride than on silver bromide and yields also much stronger brownred images after removal of the silver with Farmers solution. P-chlor-o-amino-vic.m.xylenol in aqueous sodium carbonate solution yields strong lemon-yellow images with silver chloride emulsions, while silver bromide even in alkaline solution develops much slower [to very much weaker color images. Often the developing power is intensified by the presence of a coubocyanine iodide,

pling component or this power is even created by it: p-aminophenol and dichlor-p-aminophenol do not develop the latent image on silver bromide gelatin emulsions, but do develop in a solution with m-toluylenediamine, which in itself is, of course, no developer. When using its salts in the presence of bicarbonate, a blue dye image is formed which is only slightly water-stable. Even p-amino-dimethylaniline plus bicarbonate does not develop silver bromide. In the presence of 3 nitro phenylmethylpyrazolone, however, a brick-red image is slowly-produced, but-much more quickly on silver chloride gelatine emulsion. Also coupling developers containing sodium carbonate can act selectively to a certain degree: p-aminodiamethylaniline and phenyl-J-acid Ciba yield very strong blue-green images in sodium carbonate solution on silver chloride emulsion, much weaker images on silver bromide emulsions. Similar differences exist in coupling with carbonyl-J-acid, forming dark grass-green images, 7-amino-a-naphthol couples in alkaline solution with p-aminodimethylaniline to a dark-green dye; but the images are intense only on silver chloride emulsion, while silver bromide, under the same conditions, yields only very weak dye images. The addition of NaCl or KBr also affects the selectivity. If one is not absolutely dependent on developer solutions prepared with alkali, if the developer and the possible coupling component are also soluble in water, or as most of the acid methylene compounds, in very weak alkalies (bicarbonate, borax, secondary sodium phosphate, ammonium carbonate,- sodium glycocoll etc.), one is at libertyto make the simple and coupling color developers mentioned above specific for silver chloride by section and quantity of alkali. As the examples show, the working conditions can be changed in many ways for this purpose, so that it is unnecessary to give general rules. It must be decided rather in each individual case by the nature of the experiment, with which weak alkali, with which component or with which concentration and duration of the developer the best selectivity. for silver chloride can be obtained.

It was found that the yellow-green sensitizers of the middle emulsion, as erythrcsine, rhodamine B and 6B, the dyes 777(1'-,2-diethyl- 3,4,3,4'-dibenzthiacarbocyanine iodide," 666- (2,2'-dimethyl-8-phenyl 3,4,3',4-dibenzthiacar- 555 4,4'-diphenyl-3,3'-diethyl-'I-(4-phenylthiazole ethiodide) methyl thiazolocarbocyanine iodide, and numerous other pseudocyanines and pinacyanols are rather diflicult to wash out and stable to mild oxidizing agents, also are adsorbed by reduced silver to such an extent that after the subsequent conversion into silver chloride or silver bromide certain color sensitivity remains. The middle layer may, therefore, under certain circumstances be exposed to the active kind of light and developed in color, then the two outer layers to blue or ultraviolet light, if corresponding filters are provided. These are unnecessary, if the film is coated on both sides. In order to make the regenerated silver halide of the middle emulsion accessible to ordinary light, one can also, after colored development of the two outer emulsions, remove the reduced silver or convert it into a transparent silver ferrocyanide etc. This may also be done after colored development of only one outer layer, if the other filter is still intact; or a film is used which is coated on both sides, so that also with simultaneous exposure of the two remaining layers situated on opposite sides of the' film independent development of the corresponding part color images is made possible. The two layers situated on the same side of the film are separated by a color filter, or the outer layer itself is colored as a filter. The images obtained are complementary negatives.

In certain processes, the intermediate gelatine layers are relied on, in part, to prevent difiusion. The superficial effect on the upper layer created by this can be attained much more perfectly, if first the middle layer is treated so that it is excluded, and then forms, together with the two intermediate filter layers, a neutral zone of approximately triple thickness. After this inactivation of the middle silver halide layer, individual color development of the upper layer can then be accomplished by controlled difiusion of so many kinds that in the following only the most important ones can be explained:

In reversal development, the primarily reduced silver of all three silver bromide layers can be removed or at least converted into silver ferrocyanide with potassium ferricyanide. Then the residual silver bromide of the middle layer can be exposed to yellow or red light and developed in color, provided that its color sensitivity has not been destroyed by developer and potassium ferricyanide. The residual silver bromide of the two other layers is now made developable with thiourea, stannous salt etc., or by re-exposure, and the upper part image is obtained by superficial action of a color developer by known methods of controlled difiusion, then in the usual manner the lower part image.

Similar results can be obtained with a triple layer having a silver bromide gelatine emulsion only in the middle; above.and below, however, silver chloride emulsions, preferably with pure or colored or ultra-violet absorbing intermediate gelatine layers. Other colloids less permeable to water than gelatine can be used for the latter and also for the middle silver bromide layer. The middle silver bromide layer is especially desirable in two ways, as the following examples show:

The three layers are first submitted to a nontanning developer yielding a black image in each, and this is bleached out in the usual way. Then, after selective exposure of the middle layer to light to which it is differentially sensitive, and development of this layer to an appropriate color, a color developer acting specifically on silver chloride is allowedto penetrate superficially, of course, deep enough to develop completely the latent color image of the upper layer. An effect on the lower silver chloride emulsion is eliminated with certainty, since the surface developer to reach the lowest layer has to penetrate two gelatine intermediate layers, in addition to the middle silver bromide emulsion layer. The lower part color image is then developed by prolonged action of another color developer specific for silver chloride.

Another method is to allow a properly compounded solution of potassium term-cyanide to diifuse difierentially and superficially after general ordinary development. This converts only the silver chloride of the upper layer into silver ferrocyanide, but certainly does not act on the residual silver chloride of the lower emulsion which latter is then directly developed in color. After reconversion of the silver ferrocyanide oi the upper layer into silver chloride, this is reduced with a specific color developer, then the residual silver bromide 01 the middle layer after making it developable by thiourea etc. It is less desirable to develop the residual silver bromide 01 the middle layer first in color after corresponding pre-treatment and only to then reduce the silverferrocyanide of the upper layer after conversion into silver chloride or directly with a vigorous color developer. The silver ierrocyanide oi the upper layer could be converted into the corresponding part color image either directly or after colored development of one of the two other part image, also by conversion into a colored iferrocyanidev etc. or into a mordanting body according to processes of toning and conversion.

Removal of the dye-The upper emulsion or a filter layer above it contains an insoluble yellow dye; the other two emulsions may be tanned or prepared with collodion, cellulose acetate etc. or, in films coated on both sides, only the middle emulsion or possibly also that on the other side. After general black development, the gelatine at the places containin silver and the dye in the upper emulsion are removed by persulfate, hydrogen peroxide with suitable additions, or the portions situated above them are removed. Only then the two lower emulsions are developed in color one after the other. The residual silver chloride or silver bromide of the upper emulsion may also be developed by tanning, and the yellow dye dissolved from the unhardened gelatineatter drying.

Having thus described my invention, what I claim as new and desire to be secured by Letters Patent is:

1. In a process of color photography wherein color component images are formed in each of three superposed layers by development of a silver image in each, followed by the formation of color images by reversal, the method of making the reversal images that comprises successively exposing the two outer layers to lights rendering them singly developable and developing difierently colored images in each and treating the middle layer chemically to render it developable and developing an image of a third color therein.

2. In a color photographic process in which color component images are formed in three differentially sensitized layers of a common photographic element of which the middle layer has a light absorbent filter layer on each side thereof and in which process silver images are first formed in each layer and color images are then formed therein by reversal, the steps of reexposing one of the exterior layers to light of a color absorbed by the filter between the reexposed layer and the middle layer, developing an image in color in such re-exposed layer,'re-

and in which process silver images are first formed in each layer and color images are then formed therein by reversal, the steps of re exposing one of the exterior layers to light of a color in said middle layer, and removing any remaining filter dyes and silver images, leaving only three different dye images in the three layers.

4. In a color photographic process in which color component images are formed in three layers of a common photographic element each sensitive to a diflerent spectral region, of which the middle layer has a light absorbent filter layer resistant to developing baths on each side thereof and in which process silver images are first formed in each layer and color images are then formed therein by reversal, the steps of reexposing one of the exterior layers to light of a color absorbed by the filter between the reexposed layer and the middle layer, developing an image in color in such re-exposed layer, reexposing the other of the exterior layers to light of a color absorbed by the filter between such other layer and the middle layer, developing an image in a second color in such re-exposed layer, and forming by a chemical agent an image in a third color in the middle layer.

5. In a process of color photography wherein color component, images are formed in each of three superposed gelatino-silver halide layers coated on one side of a support, by development of a silver image in each, followed by the formation of color images by reversal, the method of making the reversal images that comprises successively exposing the two outer layers to lights rendering them singly developable and developing differently colored images in each and treating the middle layer chemically to render it developable and simultaneously developing an image of a third color therein.

6. In a process of color photography wherein primary color component images are formed in each of three superposed gelatino-silver halide layers sensitive, respectively, to the red, green,

and blue spectral regions, coated on one side of rendering them singly developable and developa ing differently colored images in each and treating the originally-green-sensitive middle layer chemically to render it developable and simultaneously developing an image of a third color therein.

KARL SCHIIINZEL.

' VCER'JI'EFICATE OF oomcnon. v September a, 191 2.

KARL scnmzrm.

It hereby certified that error a ppears in the printed spectfication' of the above nu mbered patent requiring cemrection as follows; Page 14., aec- 0nd eol'mnn, line 59,for "Phenol" read --Peono1-; and that the said Lettera Ptent should be read with this cerrecti on vtherein that the same may "eonron m the record uf the me ,in the Patmt Office.

" s 1 g1 g q sealed this 20th day of October, A. D. l9l+2 Henry Van- Arsdale, (Seal) 1 Acting Commissioner of Patents. 

